Mapping California’s withering forests gives new energy to wildfire abatement

US National Park Service

Mapping California’s withering forests gives new energy to wildfire abatement

As climate change worsens, greater tree mortality across the globe will pose an increasing wildfire threat. New mapping approaches could help manage this risk.

Tubbesing, C. L., Lara, J. D., Battles, J. J., Tittmann, P. W., & Kammen, D. M. (2020). Characterization of the woody biomass feedstock potential resulting from California’s drought. Scientific Reports, 10(1), 1-14.

As global temperatures rise, most forested regions are projected to endure more frequent severe wildfires. In many cases, the increasing intensity of wildfires is a result of abnormally high amounts of dry, dead trees in a forest. Without a strategy to rapidly survey and manage dead trees on these landscapes, forested ecosystems across the globe will continue to experience unprecedented and worsening wildfires.

Wildfires across the globe emitted billions of tons of carbon dioxide into the atmosphere in 2019. At the same time, a team of researchers were developing a novel method to effectively count fire-prone dead trees across large landscapes. Previously, efforts to quantify dead trees employed aerial detection surveys to approximate total biomass. These efforts have traditionally relied upon simple models that assume tree size is identical across trees of a given species.

To enhance the accuracy of these counting exercises, Carmen Tubbesing and her colleagues combined aerial data with forest structure maps to survey the condition and number of dead trees across California in a study published in Scientific Reports. Incorporating forest structure data enables the researchers to estimate biomass at a high resolution and account for varying tree sizes across different conditions. The authors estimate that between 2012 and 2017, up to 4.8 percent of standing trees across California died, primarily as a result of severe drought and increased density of pests.

The collection and use of waste biomass for energy, particularly large woody debris, has often been considered a win-win opportunity for low-carbon, renewable electricity and wildfire mitigation. Tubbesing and her colleagues expanded upon their first-of-its-kind mapping exercise to assess the opportunity to economically remove dead trees to produce renewable electricity across the state. However, bioenergy facilities are sparse in California, and locating enough trees for energy production that also reduces fire-risk at a profitable return is a difficult task. The profitability of the process depends heavily on accurate, high-resolution assessments of the location and quality dead trees.

The researchers’ new approach to mapping the heterogeneity of dead trees at high spatial resolutions offers a fresh opportunity for California and other states in similar predicaments to turn a fire hazard into low-emissions fuel. Unfortunately, the assessment revealed that most of California’s trees are either unfit for use as energy or could not be economically retrieved and processed. Regardless, this research demonstrates the strong promise of new techniques to survey dead trees across large landscapes, and could help to inform the development of future bioenergy facilities. The data and methods developed by the authors provide a powerful tool for current bioenergy facility operators, policymakers, and foresters seeking to abate severe wildfires.